Charging a lion pack that has a BMS

[Mike_Kelly]

If I have a lion battery pack that has a built in BMS. The BMS module is managing the charge cycle and equalization of the cells.
My problem is that I bought a Renogy Boost Rover solar charge controller because it can charge "lithium" batteries.
I was not thinking when I got it that the boost controller will have no control over the charging, the BMS in t he pack will.
So then I find that the Renogy Boost Rover, in the manual, talks only about charging LIFEPO batteries, which I know nothing about.
So the bottom line is since I really don't want the solar boost controller to do anything but boost the voltage and then be a constant power source for the BMS what setting on the range of chemistry options on the solar charger will do nothing but boost and supply power vs a say lead acid setting that has multi cycle charging secenario which I don't want or need? AGM/Sealed, Gel, Flooded, and Lithium?

Thanks

 

[amberwolf]

All the options you list except Lithium are lead-acid.

You'd need to check the charging specs / curve of the Renogy to see which, if any, act like a simple LED PSU or CC/CV power supply, which is what you are asking for. Most likely the Lithium one does this, but if it doens't specify this in the manual or manufacturer spec page, you'd have to ask them.

These simply have a voltage maximum setpoint, and a current maximum setpoint. Then the resistance of the battery itself determines how much current flows, and those two plus the state of charge of the battery determines the voltage. You then set the voltage max to the full charge voltage the battery needs, and the current max to the maximum charging current you wish to use (the same or less than the max it is capable of; less for less stress on the cells and BMS).


Ideally the charging source should shut off once current drops below a certain point, rather than continuing a "trickle charge". The BMS should disconnect it's input port anyway, but if it doesn't, the current will continue to flow slightly and this is the difference between a charger and a powersupply--the PSU doesn't turn off ever, and the charger does turn off below some current draw.

 

[Mike_Kelly]

Yes I was hoping that one of the "settings" did not have a series of charge states it cycled through. I wrote to Renogy but the tech doesn't seem to understand the question and there is not much in the manual.
So what would their LiFePo setting be for? You are never going to charge a raw LIFePo battery with one of these like you would with a Lead-Acid flooded cell for instance. There is no balancing capability. All LiFePo would have BMS right? So can I assume the LiFePO setting would just supply dc to the battery BMS?

 

[amberwolf]

Pretty much any commercially produced ebike Lithium battery (of any variety) would have some form of BMS, though they do not all have balancers built in, so if you want those you either have to ask for them or make sure the one you're going to buy has them.

Other lithium batteries than ebike ones may or may not have BMS, depending on their purpose. Vehicle starter batteries may not have one, for instance. Don't know about solar bank batteries; haven't used those yet.


To know what their settings are for, you'd either have to just trust the name of the setting and use it with that kind of battery, or you'd have to find out from them what it does, exactly, or you'd have to test what it does using it with a variable load. That can either be a resistive load that you can adjust the resistance of to vary the current drawn, or a regular battery load (best).

The testing is best done using a wattmeter, so you can see the voltage and the current (and it also lets you monitor the Ah / Wh total recharged). You can use separate volt and ammeters instead, but it's less convenient and gives less info.

 

[jonyjoe303]

If you have a 10s li-ion 36 volt battery pack ( 4.20 volts x 10s = 42 volts) , 42 volts is the max you want the charger never to go over. In your situation you will use the "USER" setting of the rover controller and set the boost voltage to 42 volts or less, same with the overvoltage disconnect. All the other setting also are set at less then 42 volts as required. The 36 volt lifepo4 setting would be too high at 44.4 volts.

One thing to remember is the renogy rover boost is what will be controlling the entire charge cycle. The BMS doesnt do anything except act as a last line of defense if the voltage of the battery gets too high or too low the BMS will shutoff the power going in/out of the battery. If the BMS fails, the charger will keep charging the battery until manually disconnected. By raising the boost voltage higher or lower, you can actually control how many amps go into the battery. At 42 boost volts the battery will charge quicker, than when the boost is set to 41 boost volts. Charging at lower amps might be useful if the pack is unbalanced and you need the BMS to balance it.
As far as the BMS balancing the battery, it won't balance it unless being charged at an extremely low amps. The tiny resistors on most BMS can only bleed off 40ma which is insignificant when charging at high amps. If the battery pack is severely out of balance the BMS will always activate early and not give you a good charge.

When you start charging check to make sure the voltage on the controller is the same as what the battery is reading. If the controller is reading 40 volts, the battery terminals should also be at 40 volts, if its less than 40 volts (example 39.5 volts) then you have have a .5 volt voltage drop. A .5 volt difference will affect how many amps the battery is getting. One thing about reading the manual of the renogy is the controller doesnt have a LCD display, you might need the bluetooth dongle, it also doesnt state how to adjust the boost voltage.

You can always set the boost setting to 41 volts (4.1 volts per cell) and hopefully that won't activate the BMS which can cause problems. It will charge slower (lower amps).

 

[Mike_Kelly]

Yes Renogy seems to make better quality stuff at the low end but the manual is bad. Like you said nothing about how you set "custom levels" Their tech support is bad also. I did not know that LiFePo cells were 4.2 vs the 3.7 of Lion, I have never used them. So that is an important point, if I could figure out how to program the custom voltage. The panels are Rich 80w Cigs, two at 19.2 parallel yielding 8amps, after going thru the charge controller that should be 36v at 4amps available for charge max.
I chose the Renogy Boost Rover because of the bluetooth feature. Using it with an ebike all day I want to be able to detect problems before I find I am out of power in the middle of nowhere. I ordered a couple of MPT-7210A, also because of the display, vs Genasun or the blue MPPT unit commonly availalbe. Just in case the renogy just does not work. The MPT-7210A can specify the output current, as well as voltage, where as I don't see anything about the Renogy being able to do that.
I am also surprised that some LION BMS do not have balancing capability. I come from RC and I would never charge a battery without a smart charger with balancing. SO if you have no balance leads out of the battery and the BMS does not balance the pack how is it functional over time?
The only statement in the battery ad is:
"
Q: Do your electric bike batteries come with BMS?
A:Yes, Our batteries all with SEIKO IC BMS, with stable performance.Which can protect the battery avoid short circuit,Overcharged,Over discharge and Over current."
So thanks valuable notes for me to consider when planning the system. I bought two MOS parallel battery switches which sound like they would work fine for managing to parrallel batteries during discharge but is seems there is no way to manage two batteries and a solar charge source all active. So if I have to manually disconnect one battery to charge while I am using the other it does not seem useful to use the switch. Just charge and discharge manually switching the batteries in and out. Which over a long period risks damaging all the connectors but....

 

[amberwolf]

I did not know that LiFePo cells were 4.2 vs the 3.7 of Lion,

They're not. They're 3.2v nominal, and charge to a max of 3.4-3.65v.

Li-Ion are 3.6-3.7v nominal, and charge to a max of 4.1-4.2v.

I am also surprised that some LION BMS do not have balancing capability. I come from RC and I would never charge a battery without a smart charger with balancing. SO if you have no balance leads out of the battery and the BMS does not balance the pack how is it functional over time?

If it's made properly, of quality well-matched cells that all have identical characteristics, it won't need balancing until it age enough (over years) for the characteristics to become different. Unfortunately this isn't common for the typical ebike pack. Large EVs' batteries will be built this way, though, and some OEM ebikes' packs will be, for the better quality ones (that are also probably more expensive).

However, even an imperfectly matched pack that's made of quality cells that are still very close in characteristics will not require frequent balancing (it could be months or more).

Also, remember that balance is only that all the cells are equal voltage at some point in the charge curve (usually at full). You can rebalance cells that become different, but it doesn't actually fix anything, they still have different characteristics (resistance, capacity, etc). It does allow you to keep using more of what capacity all the cells do have.

Just charge and discharge manually switching the batteries in and out. Which over a long period risks damaging all the connectors but....

If you use connectors designed for it it'll be easier on them. For instance, Anderson SB or PP series connectors have sacrificial tips to deal with the sparking of connections, and separate conductive areas of the contacts.

There are others of various designs optimized for different types of usage.

 

[jonyjoe303]

Until everything is tested to work as advertised, the BMS, the solar controller, it would be a good idea to use an overvoltage protection relay to monitor the battery voltage and if the voltage gets to high, the protection relay will disconnect the solar panel. Thats how I run my solar system. You can find a DC overvoltage protection relay that can work at up to 99 volts for around 12 dollars, this has a small 10 amp relay which I use to trigger a much larger 30 amp automotive relay that will disconnect the solar panel. On the picture it shows a 0-40 volt protection relay, but you can find ones that read up 99 volts on ebay.
I've encountered a BMS that didn't shutoff the charging at 4.2 volts per cell, thats where the overvoltage protection relay will protect your battery from overcharging.



On the renogy boost rover, you can get a 90 volt 30 amp combometer ( about 20 dollars on ebay) and connect this between the controller and battery. This will show on a bright LED the volts and amps going into the battery in realtime. This is much better then relying on the rovers blinking lights.

 

[Mike_Kelly]

The Rover Boost has bluetooth capability to send all that data to a smartphone.
That is why I ended up in digital. Analog stuff is messy.
Thanks I will reread everything and try to digest it.
Got an answer from Renogy asking if the Rover Boost will work with my Lion battery. Not much help.
"Hi Mike Kelly,
Good day! Thank you very much for your prompt reply.
Yes, the two are compatible.
I hope this helps address your concerns. Please do let me know if you require any further assistance.
Best Regards,
Sunny"

 

[jonyjoe303]

Any solar controller that you can adjust the bulk voltage setting is compatible with Li-ion, as long as the bulk setting can be adjusted to the voltage you need. All controllers are cv/cc which is what lead,li-ion and lifepo4 need.
As far as voltage the only difference between li-ion and lifepo4 is max voltage, li-ion its 4.20 per cell and lifepo4 is 3.65 volts per cell. You multiply the cells by max cell voltage to get the bulk setting you want to set.
With the bluetooth and smartphone you should be able to set the bulk (boost) setting and then set all the other parameters using the "user" for battery type. The manual for the renogy doesnt show the steps on how to do it, but I suspect the APP for the smartphone might have its on manual/directions. When you get everything hooked up, you might want to start at a lower bulk setting, maybe 2 volt lower then you required to test everything out (40 volts instead of 42 volts).
On my 220ah lifepo4 which I can see individual cell voltage, I charge that to max voltage everyday. On my 312ah li-ion batterybank which I cannot see individual voltage, I only charge to 80 to 90 percent.

 

[Mike_Kelly]

Also I use the Renogy blue tooth module BT-1 with the blue tooth app to setup and monitor the Rover-40Put my picture in the wrong thread. Got started building.
As noted there is no imformation from Renogy about custom setting even tho they advertise it. I also don't trust their tech support after the answer that I could use the Boost for charging Lion batteries without any mention of changing the charge voltage.
Good idea that maybe there is a function in the bluetooth that leads to a custom setting.
So will keep trying and work out a test plan.
Thanks

>> I found this comment on another Rover:

"Also I use the Renogy blue tooth module BT-1 with the blue tooth app to setup and monitor the Rover-40"
Looks like your were right on the app: